Spin transition during H2O2 formation in the oxidative half-reaction of copper amine oxidases

Rajeev Prabhakar, Per E.M. Siegbahn, Boris F. Minaev, Hans Ågren

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Dioxygen reduction in the oxidative half-reaction of copper amine oxidases (CAOs) has been studied quantum chemically using the hybrid density functional theory (B3LYP). The reductive activation of dioxygen is a spin-forbidden process for which substantial kinetic O-18 (but no deuterium) isotope effects have been found experimentally. The proposed mechanism was divided into three steps, and the last step was studied for two different potential energy surfaces: the quartet and the doublet surfaces. It is suggested that dioxygen reduction occurs through a spin transition that is induced by the exchange interaction between the unpaired spins of the Cu(II) ion and the O 2- anion. The step involving this spin transition is suggested to be rate-limiting, which gives a rationalization for the puzzling experimental results when copper is substituted for other metals. The spin transition is triggered by the calculated vibronic perturbation of 5.4 (kcal/mol) Å-1, which leads to a very fast rate of 8 × 1010 s-1 for the spin transition. However, since the spin transition occurs at a calculated energy that is 18-20 kcal/mol higher than that of the reactant, this step could still be rate-limiting. The difference in the O-O bond distance between the resting state (free dioxygen) and the point of the spin transition provides an explanation for the oxygen isotope effect.

Original languageEnglish (US)
Pages (from-to)13882-13892
Number of pages11
JournalJournal of Physical Chemistry B
Volume108
Issue number36
DOIs
StatePublished - Sep 9 2004
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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